Computer simulation of hydraulic flows in a human eye

A two-dimensional computer model was developed to describe hydraulic flows inside the human eye. The flow field was described by coupled Navier-Stokes and Darcy equations. The velocity and pressure profiles in the chambers, the wall, and the vitreous body of the normal eye were obtained using the finite-element method. The model includes the filtration of fluid from the retinal capillary and its drainage through the choroid. The applications of this model include the investigation of the contribution of convection and diffusion to the transport of drugs and study of the kinetics of biodistribution in the eye.     

Computer simulation of hydraulic flows in the human eye

A two-dimensional computer model was developed to describe hydraulic flows inside the human eye. The flow field was described by coupled Navier-Stokes and Darcy equations. The velocity and pressure profiles in the chambers, the wall, and the vitreous body of the normal eye were obtained using the finite-element method. The model includes filtration of fluid from the retinal capillary and its drainage through the choroid. The applications of this model include estimation of the contribution of convection and diffusion to the transport of drugs and study of the kinetics of biodistribution in the eye.     

Efficient cloud service ranking based on uncertain user requirements

In a cloud computing environment, there are many providers offering various services of different quality attributes. Selecting a cloud service that meets user requirements from such a large number of cloud services is a complex and time-consuming process. At the same time, user requirements are sometimes described as uncertain (sets or intervals), something which should be taken into account while selecting cloud services. This paper proposes an efficient method for ranking cloud services while accounting for uncertain user requirements. For this purpose, a requirement interval is defined to fulfill uncertain user requirements. Since there are a large number of cloud services, the services falling outside the requirement interval are filtered out. Finally, the analytic hierarchy process is employed for ranking. The results evaluate the proposed method in terms of optimality of ranking, scalability, and sensitivity analyses. According to the test results, the proposed method outperforms the previous methods.

     

基于规划支持系统的环境影响评价

如何在土地利用规划过程中考虑环境影响是土地利用规划中的一个难点问题.在定义活动、影响域、功能区、敏感度等概念的基础上,详细论述了土地利用规划支持系统(strate-gic tool for integrating environmental aspects in planning procedures,STEPP)将环境影响融入土地规划设计的过程.该系统是在ArcView GIS二次开发语言Avenue上开发的规划支持系统,可以方便规划相关人员在系统平台上进行信息交互,并在空间上直观、定量地表现规划过程中的环境影响及其变化.以荷兰埃德和维纳多市之间的城乡结合部为研究区进行案例研究,结果表明,该系统的定义和评价过程能较好地将环境影响融入到规划设计过程中,适时、直观地反映规划措施对环境的影响,方便了规划参与者参与规划过程,为决策者制定科学规划提供了依据.最后,对该系统如何应用于我国的规划环境影响评价提出了建议.     

User requirements on CT-based computed dose planning systems in radiation therapy. Presentation of 'check lists'

The expanding use of computers in radiation therapy procedures, especially the rapidly increasing use of digital CT-information, necessitates the coordination of the different systems in order to facilitate their developments. In order to define necessary demands for tomorrow a Nordic cooperation was initiated 1981 by NORDFORSK (Nordic co-operative organization for applied research), and a group of physicians and physicists having their daily work in this field of medicine and physics was invited to produce a report on 'User requirements on CT-based computed dose planning systems on radiation therapy'. The work has been done within the frame of NORDFORSK's activities and has been independent of the existing commissions and associations in the radiology field, but it has taken into consideration recommendations that have been given by or are being produced by other organizations. This report is a short summary of the complete paper which will be published in Acta Radiologica. The aim of this short version is to get an early presentation of the 'requirement lists' (see Appendix) which we think are of immediate importance.     

Quick selection of representative protein chain sets based on customizable requirements

MOTIVATION: Protein structure classification has been recognized as one of the most important research issues in protein structure analysis. A substantial number of methods for the classification have been proposed, and several databases have been constructed using these methods. Since some proteins with very similar sequences may exhibit structural diversities, we have proposed PDB-REPRDB: a database of representative protein chains from the Protein Data Bank (PDB), which strategy of selection is based not only on sequence similarity but also on structural similarity. Forty-eight representative sets whose similarity criteria were predetermined were made available over the World Wide Web (WWW). However, the sets were insufficient in number to satisfy users researching protein structures by various methods. RESULT: We have improved the system for PDB-REPRDB so that the user may obtain a quick selection of representative chains from PDB. The selection of representative chains can be dynamically configured according to the user's requirement. The WWW interface provides a large degree of freedom in setting parameters, such as cut-off scores of sequence and structural similarity. This paper describes the method we use to classify chains and select the representatives in the system. We also describe the interface used to set the parameters.     

Design of small molecule-responsive microRNAs based on structural requirements for Drosha processing

MicroRNAs (miRNAs) are prevalent regulatory RNAs that mediate gene silencing and play key roles in diverse cellular processes. While synthetic RNA-based regulatory systems that integrate regulatory and sensing functions have been demonstrated, the lack of detail on miRNA structure-function relationships has limited the development of integrated control systems based on miRNA silencing. Using an elucidated relationship between Drosha processing and the single-stranded nature of the miRNA basal segments, we developed a strategy for designing ligand-responsive miRNAs. We demonstrate that ligand binding to an aptamer integrated into the miRNA basal segments inhibits Drosha processing, resulting in titratable control over gene silencing. The generality of this control strategy was shown for three aptamer-small molecule ligand pairs. The platform can be extended to the design of synthetic miRNAs clusters, cis-acting miRNAs and self-targeting miRNAs that act both in cis and trans, enabling fine-tuning of the regulatory strength and dynamics. The ability of our ligand-responsive miRNA platform to respond to user-defined inputs, undergo regulatory performance tuning and display scalable combinatorial control schemes will help advance applications in biological research and applied medicine.     

Numerical simulation of aortic bifurcation flows: The effect of flow divider curvature

Two dimensional steady flow calculations in computational regions obtained from radiographs of human aortic bifurcations correlate well with unsteady measurements of wall shear in flow-through casts of the same vessels. The results suggest that wall slope may be an important factor affecting the variability of shear along the medial walls of this arterial segment. If extremes of shear stress promote atherogenesis, then variations in the curvature of the proximal iliac arteries may affect the susceptibility of these vessels to vascular disease on their medial aspect.     

Taste psychophysics based on a simulation of human drinking

Taste stimulation during human drinking is approximated by alternatestimulation of the tongue with a stimulus liquid and a secondliquid. Such stimulation produces no significant sensory adaptationof taste, in contrast to continuous stimulation with the stimulusliquid. The absence of a reduction over time in judged tasteintensity holds up under variations in flow duration of thetwo liquids (1 sec to 3 sec), stimulus compound NaCl or Na-saccharin),stimulus concentration (2 mM Nasaccharin; 100 mM-500 mM NaCl),or subjects (29). Pulsatile, alternating taste stimulus presentationrepresents a model of taste relevant to human drinking. ¹With the technical assistance of D. Baron and L. Snyder.     

基于过程的小麦茎鞘夹角动态模拟

基于不同株型品种和不同密度处理的小麦田间试验,连续观察并记录各处理不同叶位叶鞘与主茎之间的夹角,进一步利用系统分析方法和动态建模技术,构建基于过程的小麦叶片茎鞘夹角的动态模拟模型.结果表明:小麦茎鞘夹角随叶片生育进程不断加大,并随密度的增大而减小;从第2叶开始,最大茎鞘夹角随叶位的增加而减小.所建模型利用Logistic方程描述叶片茎鞘夹角随生育进程的动态变化过程,使用分段函数描述最大茎鞘夹角随叶位的动态变化,引入品种参数(第2叶茎鞘夹角的最大值)量化了茎鞘夹角在不同品种之间的差异,并利用基本苗量化了密度对茎鞘夹角的影响.基于独立的田间试验资料对所建模型进行测试与检验,结果显示茎鞘夹角模拟值与观测值之间的均方根差为1.7°.表明模型对小麦主茎叶片茎鞘夹角的动态变化过程具有较好的预测性,为小麦生长过程的可视化表达奠定了技术基础.     

Numerical simulation of streaming potentials due to deformation-induced hierarchical flows in cortical bone

Bone is a very dynamic tissue capable of modiA,fing its composition, microstructure, and overall geometry in response to the changing biomechanical needs. Streaming potential has been hypothesized as a mechanotransduction mechanism that may allow osteocytes to sense their biomechanical environment. A correct understanding of the mechanism for streaming potential will illuminate our understanding of bone remodeling, such as the remodeling associated with exercise hypertrophy, disuse atrophy, and the bone remodeling arounid implants. In the current research, a numerical model based on the finite element discretization is proposed to simulate the fluid flows through the complicated hierarchical flow system and to calculate the concomitant stress generated potential (SGP) as a result of applied mechanical loading. The lacunae-canaliculi and the matrix microporosity are modeled together as discrete one-dimensional flow channels superposed in a biphasic poroelastic matrix. The cusplike electric potential distribution surrounding the Haversian canal that was experimentallv observed and reported in the literature earlier was successfully reproduced by the current numerical calculation.     

Applications of MCNP simulation in treatment planning: a comparative study

Radiation and Environmental Biophysics - Monte Carlo codes have been used for approximately 80 years to solve various problems in medical physics. In this paper, the importance of the...     

Numerical simulation of LDL mass transfer in a common carotid artery under pulsatile flows

Symmetrical 30-60% stenosis in carotid artery with a semi-permeable wall under steady/unsteady flows for Newtonian/non-Newtonian fluids is investigated numerically. The results show that the unsteadiness of blood flow, blood pressure rise and LDL component size increase the luminal concentration, LC, of the surface. The maximum LC occurring immediately after the separation point and the non-Newtonian fluid predicts higher LDL accumulation. LC decreased as the recirculation length is increased and reaches maximum at 40% stenosis. This process is used to estimate the time-dependent growth of the arterial wall.     

Structural requirements of ceramide and sphingosine based inhibitors of mitochondrial ceramidase

The effects of structural analogues of ceramide on rat brain mitochondrial ceramidase (mt-CDase) were investigated. Design of target compounds was mainly based on modifications of the key elements in ceramide and sphingosine, including stereochemistry, the primary and secondary hydroxyl groups, the trans double bond in the sphingosine backbone, and the amide bond. Mt-CDase was inhibited by (1) all stereoisomers of D-erythro-ceramide (D-e-Cer) with an IC50 of 0.11, 0.21, and 0.26 mol % for the L-threo, D-threo, and L-erythro isomers, respectively; (2) all stereoisomers of sphingosine with IC50 ranging from 0.04 to 0.14 mol %, N-methyl-D-erythro-sphingosine (N-Me-Sph, IC50 0.13 mol %); and (3) D-erythro-urea-C16-ceramide (C16-urea-Cer IC50 0.33 mol %). The enzyme was not inhibited by N-methyl ceramide (N-Me-C16-Cer), 1-O-methyl ceramide (1-O-Me-C16-Cer), 3-O-methyl ceramide (3-O-Me-C16-Cer), cis-D-erythro ceramide (cis-D-e-C16-Cer) and 3-O-methyl-D-erythro-sphingosine (3-O-Me-Sph). It was less potently inhibited by D-erythro-sphinganine (D-e-dh-Sph, IC50 0.20 mol %), D-erythro-dehydro sphingosine (D-e-deh-Sph, IC50 0.25 mol %), (2S)-3-keto-sphinganine (3-keto-dh-Sph, IC50 0.34 mol %), (2S) 3-keto-ceramide (3-keto-C16-Cer, IC50 0.60 mol %), and ceramine (C18-ceramine, IC50 0.62 mol %), 1-O-methyl-D-erythro-sphingosine (1-O-Me-Sph), cis-D-erythro-sphingosine (cis-D-e-Sph), (2S)-3-ketosphingosine (3-keto-Sph), (2S)-3-keto-dehyrosphingosine (3-keto-deh-Sph), and N,N-dimethyl-D-erythrosphingosine (N,N-diMe-Sph) were weak inhibitors whereas ceramide-1-phosphate (Cer-1-P) and sphingosine-1-phosphate (Sph-1-P) stimulated the enzyme. Thus, for inhibition, the enzyme requires the primary and secondary hydroxyl groups, the C4-C5 double bond, the trans configuration of this double bond, and the NH-protons from either the amide of ceramide or the amine of sphingosine. Therefore, these results provide important information on the requirements for ceramide-enzyme interaction, and they suggest that ligand interaction with the enzyme occurs in a high affinity low specificity manner, in contrast to catalysis which is highly specific for D-erythro-ceramide (D-e-Cer) but occurs with a lower affinity. In addition, this study identifies two competitive inhibitors of mt-CDase; urea-ceramide (C16-urea-Cer) and ceramine (C18-ceramine) that may be further developed and used to understand the mechanism of mt-CDase in vitro and in biologic responses.     

Impact of missing genotype data on Monte-Carlo simulation based haplotype analysis

In the context of haplotype association analysis of unphased genotype data, methods based on Monte-Carlo simulations are often used to compensate for missing or inappropriate asymptotic theory. Moreover, such methods are an indispensable means to deal with multiple testing problems. We want to call attention to a potential trap in this usually useful approach: The simulation approach may lead to strongly inflated type I errors in the presence of different missing rates between cases and controls, depending on the chosen test statistic. Here, we consider four different testing strategies for haplotype analysis of case-control data. We recommend to interpret results for data sets with non-comparable distributions of missing genotypes with special caution, in case the test statistic is based on inferred haplotypes per individual. Moreover, our results are important for the conduction and interpretation of genome-wide association studies.